Here is the retail locator on the Dickies site. It also seems to indicate that they are available at WalMart, JC Penney, and K Mart… which I assume are nationwide retailers.
None of the retail locations through the site seem super promising… they might sell some Dickies products but not pants. There is no K-Mart, JC Penney or Wal-Mart in SF AFAIK.
Walmart does sell Dickie pants, because they make great work pants. They don’t always have them in stock, however.. I’ve bought them at stores that sell work and school uniforms.